Linear motor and linear compressor including said motor

ABSTRACT

A linear motor and a linear compressor including said motor. The linear motor comprises a set of inner laminations ( 90 ), forming the stator, mounted around the outer circumference of a fixed member ( 60 ), and a set of outer laminations ( 30 ) mounted spaced from the inner laminations ( 90 ). An actuator ( 85 ) is connected to a movable member ( 80 ) and carries a magnet member ( 86 ) in the space defined between the inner laminations ( 90 ) and the outer laminations ( 30 ). The upper ends of the inner laminations ( 90 ) and outer laminations ( 30 ) are connected by a connecting element ( 100 ) made of a non-magnetic material, in order to stabilize the laminations and serve as a suspension mounting for the set of outer laminations ( 30 ). Application of electric current to a coil ( 95 ) causes the actuator ( 85 ) to move and carry the movable member ( 80 ) with it. The fixed member ( 60 ) is defined by the cylinder of the compressor and the movable member ( 80 ) by the piston, which is reciprocated inside the cylinder to compress a refrigerant gas, and the connecting element ( 100 ) does not contact the cylinder. This arrangement does not require any special configuration of the cylinder or use of an additional plate to provide the connection to the outer laminations.

FIELD OF THE INVENTION

[0001] The present invention relates to a linear motor presenting asimplified mounting of the laminations of the motor, in order to improvethe efficiency of said motor, particularly when applied to linearcompressors of small refrigeration systems.

BACKGROUND OF THE INVENTION

[0002] Electric linear motors are well known devices, in which one of acoil or magnet element is mounted to a fixed member, and the otherelement is mounted to a member to be moved. Electric current is appliedto the coil, which generates magnetic lines of force to interact withthe magnet to produce linear motion of the movable member. Such electriclinear motors are generally used in refrigeration compressors in whichthe movable member is defined by the piston of the compressor and themagnet is mounted to said piston. The coil is fixedly mounted to anexternal portion of the compressor structure that forms the cylinder,inside which the piston is reciprocated.

[0003]FIG. 1 of the appended drawings illustrates a prior art linearcompressor of the type disclosed in U.S. Pat. No. 5,945,748. In thisknown prior art construction, there is provided a hermetic shell 10,within which is mounted a cylindrical inner cup 20 that defines apredetermined inner space. A set of outer laminations 30 for a linearmotor is affixed to the inner face of the inner cup 20. A disk shapedcover plate 40 has a hole in a center portion thereof and is connectedto a flange 61 that is incorporated to the upper end of a cylinder 60and to upper end portions of both the inner cup 20 and outer laminations30. A lower cover 50, which is also disk shaped, is connected to thelower end portion of the inner cup 20. An upper portion of the cylinder60 extends through the open center portion of the cover plate 40, and avalve system 70 is mounted to the center of the upper portion of thecylinder 60 to tightly cover the hole through which the upper portion ofthe cylinder 60 extends. A conventional valve plate having suction anddischarge valves can also be used. Inside the cylinder 60 is mounted apiston 80 which, upon being reciprocated by the linear motor, compressesa refrigerant gas in a known manner. A set of inner laminations 90 ofthe linear motor is mounted around a portion of an outer circumferentialsurface of the cylinder 60, said internal laminations 90 maintaining apredetermined spacing from the set of outer laminations 30.

[0004] A coil 95, of toroidal shape, is located in a cut-out portion ofan outer circumferential surface of the inner laminations 90, and theends of the coil 95 are connected to lead wires (not shown) that supplyelectric current to the coil 95. If desired, the coil 95 can also belocated on the set of outer laminations 30. A connecting member in theform of a disk connects the lower end of the piston 80 to a cylindricalactuator 85, to the upper end of which is attached a magnet member 86usually formed by a plurality of permanent magnets (not shown). Themagnet member 86 moves in the space between the sets of outerlaminations 30 and inner laminations 90.

[0005] As seen from FIG. 1, the linear motor includes the set of outerlaminations 30, the set of inner laminations 90 carrying the coil 95,and also the actuator 85, to which the magnet member 86 is attached.

[0006] Inner helical springs 66 are provided between the connectingmember 65 and a support 68 that is affixed to the bottom of the set ofinner laminations 90 to elastically support the reciprocation of thepiston 80. Outer helical springs 67 are disposed between the connectingmember 65 and the lower cover 50 to support the compressor as the piston80 reciprocates. At least one refrigerant gas path 80 a is providedalong an upper portion of the cylinder 60 for admitting refrigerant gasinto the latter at a determined position of the piston 80.

[0007] In the operation of the compressor illustrated in FIG. 1, whenelectric current is supplied to the coil 95, the magnet member 86,mounted to the actuator 85, reacts with the magnetic lines of force andreciprocates the actuator 85 in a straight line between the innerlaminations 90 and the outer laminations 30, whereby the piston 80 isreciprocated in the cylinder 60 as a function of the correspondingdisplacement of the actuator 85. The refrigerant gas flows into thecylinder 60 through the refrigerant gas paths 80 a provided in thecylinder 60. The refrigerant gas compressed in the cylinder 60 isdischarged through the valve system 70, and the above describedoperation is repeatedly performed.

[0008] The inner laminations 90 may be mounted to the cylinder by usingany one of the constructions presently known, such as the oneillustrated in FIG. 1. For example, there can be provided a moldedbracket member mounted to the cylinder and carrying the innerlaminations 90, these laminations having a cut-out in the outer surfacesthereof for lodging the coil 95.

[0009]FIG. 1A illustrates a type of mounting that can be used formounting the outer laminations 30. This figure illustrates amodification of an arrangement shown in said US patent. The outerlaminations 30, made of a magnetic metal, such as iron or steel, areradially disposed relative to the center of the compressor. A tubularframe 25 is mounted internal of the wall of the inner cup 20 and carriesa shelf 26 onto which is mounted the lower end of each outer lamination30, and the tubular frame 25 is further provided with an upper bracket27 to connect the upper end of the outer laminations 30. Nevertheless,it should be understood that any suitable mounting arrangement might beused for adequately securing the outer laminations 30 to the wall of theinner cup 20.

[0010] As seen in the compressor of FIG. 1, the cylinder 60 is formedwith a flange 61 extending radially outwardly from the top of thecylinder 60, and the cover plate 40 provides a connection between theflange 61 of the cylinder 60 and the outer laminations 30. As describedbelow, this known construction gives rise to various problems.

[0011]FIG. 2 shows a part of another type of prior art compressor formedby a cylinder 60, to whose outer face is affixed, by glue or any otherfixing means, a linear motor, whose stator comprises inner laminations90 having an external cut-out for housing a toroidal coil 95, as alreadydescribed in relation to FIG. 1. The upper ends of a set of outerlaminations 30 are directly affixed, by glue, welding or any otherfixing means, to the inner surface of an external portion of a flange 61incorporated to the cylinder 60 and extending radially outwardlytherefrom, in order to provide a suspension mounting to the outerlaminations 30. The lower surface of the flanges 61 also contacts thetops of the inner laminations 90. Thus, there is provided a directconnection between the flange 61 of the cylinder 60 and the outerlaminations 30 and the inner laminations 90.

[0012] Heretofore the linear motor has been described as used in alinear compressor. However, such linear motors also find use in otherdevices. For example, a stationary bushing can replace the cylinder 60of the compressor and the piston of the latter can be replaced by ashaft that can be reciprocated to perform a determined work as thelinear motor operates. Such other devices may require arrangements formounting the inner and outer laminations, and may present variations inthe structural configurations thereof in relation to those illustratedin FIGS. 1, 1A and 2. However, all these known variations use a directconnection between the three components that are, (or correspond to, inother devices) the cylinder 60 with its flange 61, the inner laminations90, and the outer laminations 30 of the linear motor.

[0013] Such constructions, which are described particularly for thelinear compressor, but have equivalent components in other usefuldevices, have the following disadvantages:

[0014] a large amount of material is required for constructing thecylinder, since the cylinder must incorporate its radially outwardlyprojecting flange 61. Moreover, in the embodiment illustrated in FIG. 1,it is further required the provision of the cover plate 40.

[0015] the cylinder must be made of a non-magnetic material, in order toavoid the flow of magnetic lines of force through the structure. Thiswould generate Foucault currents producing heat and energy loss.

[0016] the non-magnetic materials for producing the cylinder are usuallyof the austenitic type, or of various types of stainless steel oraluminum, among others, and all such materials being relativelyexpensive.

[0017] the construction of the cover plate 40 and the flange 61 of thecylinder 60 present a large surface, causing undesired irradiation ofnoise.

[0018] a large number of machining operations is needed to form thecylinders illustrated in FIGS. 1 and 2, as well as a large amount ofinvestment in equipment to produce the cylinders.

[0019] some non-magnetic materials used to produce the cylinder areinadequate for the components to be subjected to friction, as it occurs,for example, between the reciprocating piston and the cylinder, orbetween the reciprocating shaft and the stationary bushing, makingnecessary, in certain cases, to use a sleeve of a harder material forthe cylinder or bushing. This makes the mounting operation moredifficult, increasing the cost of the final product.

OBJECTS OF THE INVENTION

[0020] An object of the invention is to provide a linear motor havinginner laminations 90 and outer laminations 30 connected by a ring membermade of non-magnetic material and without using any connection to afixed member inside which another member is reciprocated.

[0021] Yet another object of the invention is to provide a linear motorfor a linear compressor formed by a set of inner laminations mounted tothe cylinder, and a set of outer laminations, with the inner and outerlaminations being connected by a non-magnetic connecting ring thatstabilizes the laminations but does not make contact with any part ofthe compressor cylinder.

[0022] Still a further object of the invention is to provide a linearmotor for a linear compressor that does not require any direct fixationto the cylinder to mount the laminations of the linear motor.

SUMMARY OF THE INVENTION

[0023] The linear motor of the invention is described as used with alinear compressor having a cylinder, within which a piston isreciprocated by a linear motor to compress refrigerant gas. The linearmotor is formed by a set of inner laminations, defining a stator andmounted around the outer circumference of the cylinder, and a toroidalcoil, which is constructed to receive electric current, is carried bythe inner laminations. A set of outer laminations is mounted around theinner surface of a cup, inside which the compressor is housed. In somedevices, there can be provided a second coil carried by the outerlaminations, or the coil can be provided only in the set of outerlaminations. An actuator is connected to the lower end of the piston andcarries a magnet member in the space between the inner and outerlaminations. Upon application of current to the coil, the actuator iscaused to reciprocate, carrying the piston with it.

[0024] The upper ends of the inner and outer laminations are connectedby a connecting ring made of a non-magnetic material that does notcontact the cylinder. The connecting ring serves as a suspensionmounting for the outer laminations, since the inner laminations aremounted to the fixed cylinder. This also provides stabilization for thesets of laminations. This arrangement does not require any specialconfiguration of the cylinder or use of a separate cover plate.Therefore, the proposed solution is simple and inexpensive to make, andit provides additional advantages in that the cylinder and piston can bemade of less expensive materials, such as cast iron or steel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other objects and advantages of the present invention will becomemore apparent upon reference to the attached drawings, in which:

[0026]FIG. 1 is an elevational cross-sectional view of a firstembodiment of a prior art linear compressor;

[0027]FIG. 1A is an elevational view of one type of mounting arrangementfor the outer laminations of a linear motor according to the prior art;

[0028]FIG. 2 is an elevational cross-sectional view of a portion of alinear compressor according to another embodiment of the prior art; and

[0029]FIG. 3 is an elevational cross-sectional view of a portion of alinear compressor constructed according to the subject invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0030] The linear motor of the present invention will be described belowwith respect to its application to a linear compressor. FIG. 3 shows anembodiment of the invention in which the same reference numbers are usedfor the same components previously described. According to theinvention, the linear motor has a stator formed by a set of innerlaminations 90 mounted onto the outer surface of a cylinder 60. Like inthe compressor of FIG. 2, the inner laminations 90 have cut-outs in theouter surfaces thereof to house a coil 95, to which electric current issupplied. As illustrated, the cylinder 60 is of smaller size and of lesscomplicated construction as compared to the cylinder 60 of theconstructions illustrated in FIGS. 1 and 2, since the flange 61 is nolonger required.

[0031] A set of outer laminations 30 secures, inferiorly, an upperportion of the inner cup 20. A connection is provided between the upperends of the inner laminations 90 and the upper ends of the outerlaminations 30 by a connecting element 100, which is shown in the formof a ring. The connecting element 100 may be a flat molded or stampedpiece that is fastened to the upper ends of each of the innerlaminations 90 and those of the outer laminations 30 by any suitabletechnique, such as by using an adhesive or by welding, depending on thematerials used for the connecting element. The connecting element 100operates as a suspension type mounting for the set of outer laminations30, that is, it is secured to the set of inner laminations 90, which inturn is mounted to the stationary cylinder 60. Thus, the outerlaminations 30 can be mounted without the use of a bracket such as thatillustrated in FIG. 1. The connecting element 100 is made of anon-magnetic material, such as stainless steel, plastic, aluminum, etc.The connecting ring 100 is preferably provided with through holes 107opened to the space within which the magnet member 86 moves in order topermit the passage of gas that is compressed by the magnet member 86 insaid space.

[0032] The construction of the present invention has several advantages,among which the following may be mentioned:

[0033] there is achieved a reduction in the size of the cylinder, sincethe flange 61 is no longer required, as contemplated in FIGS. 1 and 2.Also, no separate cover 40 is required, as contemplated in thecompressor of FIG. 1.

[0034] the absence of the cylinder flange and/or cover plate eliminatesa source of noise.

[0035] the cylinder 60 may be made of a magnetic material, such as steelor cast iron, which is less expensive than a non-magnetic material. Suchmetals are also more structurally reliable when subjected to friction bythe reciprocating piston, which, in this case may also be made of steelor cast iron.

[0036] the linear motor remains magnetically insulated from thecylinder, since the connecting element 100 is of non-magnetic material.Therefore, no Foucault currents are generated.

[0037] the mounting of the various elements is simplified.

[0038] the production of the cylinder, as compared to the structures ofthe prior art cylinder, is simplified.

[0039] While the linear motor has been described to drive the piston ofa linear compressor in the disclosed embodiment of the invention, itshould be understood that this motor construction also can drive adifferent element instead of the piston, for example, a shaft of anequipment that reciprocates within a bushing in place of the compressorcylinder. In such devices, there is no need to provide a flangeincorporated to the bushing or the cylinder to connect the laminations.

[0040] Specific features of the invention are shown in a figure of thedrawings for convenience only, as each feature may be combined withother features according to the invention. Alternative embodiments willbe recognized as possible by those skilled in the art and are intendedto be included within the scope of the claims. Accordingly, the abovedescription should be construed as illustrating and not limiting thescope of the invention. All such obvious changes and modifications arewithin the scope of the appended claims.

1. A linear motor, having a stator formed by a set of inner laminations(90) carrying a coil (95) and attached to a fixed member (60), and a setof outer laminations (30) spaced from the inner laminations (90), and amagnet element (86) carried by an actuator (85) that is connected toreciprocate a movable member (80) within the fixed member (60) whenelectric current is applied to the coil (95), characterized in that itcomprises a connecting element (100) in the form of a ring, connectingthe outer laminations (30) and the inner laminations (90) saidconnecting element (100) being spaced from and does not contact thecylinder (60) of the compressor.
 2. The linear motor as set forth inclaim 1, characterized in that the connecting element (100) connects thetop portions of the outer laminations (30) with the top portions of theinner laminations (90).
 3. The linear motor as set forth in claim 1,characterized in that said connecting element (100) is made of anon-magnetic material.
 4. The linear motor as set forth in claim 2,characterized in that said connecting element (100) has through holes(107) communicating with the space defined between the inner laminations(90) and the outer laminations (30).
 5. A linear compressor includingthe linear motor as defined in claim 1, characterized in that said fixedmember (60) is a cylinder (60) of a compressor, said movable member (80)being defined by a piston which is reciprocated in the cylinder (60) bythe linear motor.
 6. The linear motor as set forth in claim 2,characterized in that said connecting element (100) is made of anon-magnetic material.
 7. A linear compressor including the linear motoras defined in claim 2, characterized in that said fixed member (60) is acylinder (60) of a compressor, said movable member (80) being defined bya piston which is reciprocated in the cylinder (60) by the linear motor.8. A linear compressor including the linear motor as defined in claim 3,characterized in that said fixed member (60) is a cylinder (60) of acompressor, said movable member (80) being defined by a piston which isreciprocated in the cylinder (60) by the linear motor.
 9. A linearcompressor including the linear motor as defined in claim 4,characterized in that said fixed member (60) is a cylinder (60) of acompressor, said movable member (80) being defined by a piston which isreciprocated in the cylinder (60) by the linear motor.